Reports of an association between anal cancer and homosexuality in men predated the AIDS epidemic, with the incidence of anal cancer being estimated as high as 35/100,000 among homosexual men a rate approaching that of cervical cancer before pap screening. Since the development of cancer or precancer and expression of human papilloma virus (HPV) infection (the suspected causal agent of many genital and anal squamous cancers) are known to be increased in the presence of impaired immunity, we postulate that with the spread of HIV infection, anal intraepithelial neoplasia (AIN) and anal cancer are becoming increasingly common among homosexual men. As therapies are developed that prolong the life of HIV infected patients associated malignancy and premalignancy will become a significant problem. In order to assess the potential magnitude of the problem and to study the relationship of HIV and other risk factors to AIN, we propose a cross sectional study of a group of sexually active homosexual men who are either currently infected with HIV or at risk for HIV infection. We will determine the prevalence of specific types of current anal HPV infection and of AIN, and study their relationship to HIV infection and immune status. Subjects will be interviewed regarding basic demographic characteristics, sexual behavior and history, and medical history. A general physical exam, as well as an anaoscopic exam for clinically colposcopically visible anal or penile warts will be performed. Blood will be collected for determination of T cell subsets, and serologic evidence of exposure to HIV, syphilis, HSV 1 & 2, C. trachomatis, as well as specific types of HPV. Cytotologic samples of the anal epithelium as well as samples for detection of HPV DNA will be collected. Patients with anal lesions, cytologic evidence of AIN or anal HPV DNA will be scheduled for biopsy and appropriate treatment.